Method and apparatus for making fluorine



Feb. 26 1924.:

F. C. MATHERS ET AL METHOD AND APPARATUS FOR MAKING FLUORINE Filed July'7, 1919 z r r W 3 A if 3 Lmmm m fi 1 will I AH IIII 3 I W ulmiizmgnzl MM 1W FRANK C. MATHERS, OF BLO'OMINGTON, INDIANA, ,AND BURIR HUMISTON, OFWIL- I MINGTON, DELAWARE.

METHOD AND APPARATUS FOR MAKING FLUORINE.

Application filed July 7, 1919. Serial No. 809,254.

To all whom it may concern:

Be it known that we, FRANK C. MATHERS and Bum: HUMISTON, citizens of theUnited States, and residing at Bloomington, In-

6 diana, and Wilmington, Delaware, respectively, have invented certainnew and useful Improvements in Methods and Apparatus for MakingFluorine, of which the following is a specification.

This invention relates to a novel method and apparatus for makingfluorine.

()ne of the objects of this invention is to provide a method and meansfor producing fluorine on a satisfactory commercial basis and on aslarge a scale as desired, and

to eliminate disadvantageous conditions existing in the prior processes.

Another object of this invention is to provide an apparatus for makingfluorine wherein the heating is so distributed that no excessive localheating results but the electrolyte is heated in. a substantially,uniform manner.

Another object of this invention is to zfi'provide the apparatus withmeans for avoiding the necessity of using an excessive electromotiveforce for decomposing the electrolyte. I

Reference is to be had to the accompanyso ing drawing in which thepreferred form of our apparatus is shown.

The vessel (1) contains the electrolyte (2) in which the diaphragm (3)is partly submerged. This diaphragm is provided.

with openings or slots (4) near the lower portion thereof. Thevessel.(1) and diaphragm (3) should be made of material which is notseriously attacked by either hydrofluoric acid or by fluorine. In our4.0 preferred form of apparatus we make these parts of graphite, carbonor copper; the

rarbon, graphite,-or copper vessel serving as the cathode.

The anode (5), which we have found should preferably be made ofgraphite, al-

though carbon may'be used, is located with in the diaphragm and in theupper portion thereof a copper lead (6) is secured and this passes outthrough the top (7) of the diaphragm (3). The fluorine which is evolvedat the anode passes out by the way of the exit (8 In order to preventthe fluorine from escaping through the top (7) of the diaphragm, and tokeep the anode as in proper position within the vessel and insulatedfrom the vessel (1) and diaphragm (3), we have provided the top (7) witha gland (8) and nut (9). A washer (10) made of fluorspar or othermaterial which is resistant to the action of fluorine and possessesinsulating properties, is placed within the gland and serves to supportthe lead (6) and anode (5), the shoulders (11) on the lead (6) restingupon the washer (10). Powdered fluorspar or other insulating materialwhich will withstand the action of fluorine is placed within the gland(8) and over the washer (10) and another washer (12), preferably made ofmaterial similar to that of (10) or of fiber since fluorine does notreach this point, is placed over the. powdered material which is heldclosely and firmly around the upper portion (13) of the lead (6) bymeans of the cap (9) screwed down on the gland (8). The positiveterminal (14) of the electrolyzing current is joined to the lead (6),the negative terminal (15) being joined directly to the copper vessel(1) serving as a cathode.

Local heating of the bath, such as is obtained with a Bunsen burner, isobjectionable because where the heat is localized there is overheatingand this will cause the containing vessel to be attacked by theelectrolyte. 35

We overcome the disadvantage of local heating by winding a suitablewire, such as nichrome wire (16) around the vessel (1) and insulatingthe wire from the vessel by means of asbestos paper (17). To preventloss of heat by radiation the wires (16) are surrounded by asbestos wool(18) and asbestos paper (19). By passing an electric current through thewire, the vessel (1) and its contents will be heated and the heat willbe uniformly distributed instead of localized.

The preferred form of electrolyte which we use is acid potassiumfluoride, but it should be understood that other fluorides or 100compounds of fluorine or mixtures thereof may be used which are notattacked by fluorine and which melt at a temperature at which thegraphite anode and the containing vessel are not seriously attacked by10 fluorine. Anhydrous potassium acid fluoride melts at approximately220 C. and at this temperature decomposes but slightl A fresh bathprepared from KF and H generally contains some water which is removed byelectrolyzing at a low current density before fluorine is obtained. Ifthe current density is too high, polarization will result and the E. M.F. will rise to as much as 50 to 60 volts. A current of from 2 to 3amperes per square decimeter is first passed through the electrolyte toremove any water contained therein. anode gas shows the presence offluorine a much higher current density is used to effect electrolysis offluorine. After the water is removed raising the current density doesnot produce polarization.

A satisfactory current density has been found to be 10 amperes persquare decimeter, and an E. M. F. of 12'to 15 volts.

After the bath is subjected to electrolysis for a considerable length oftime the electrolyte becomes viscous owing to the accumulation of KF andCuF where a copper vessel, diaphragm or false bottom is used. Thisresults in frothing of the bath around the anode and may be remedied byremoving the salt and grinding same and then-adding HF. In replenishingthe salt with acid it is well to have a reasonable excess of-acid. Atintervals it will be necessary to dissolve the bath in water and filterto remove accumullated copper fluoride and organic materia The bathshould not be heated so low that the electrolyte will be too viscous,neither should it be heated so highly that HF will distil off toorapidly. At higher temperatures the conductivity of the bath isincreased appreciably, but the loss of HF 0E- sets this advantage.

We provide the diaphragm with a false bottom (20) made of graphite,carbon or copper which prevents the hydrogen evolved at the bottom ofthe electrolyzing vessel from rising to the inside of the diaphragmwhere it would unite with the fluorine evolved at the anode. Ihefluorine evolved at the anode collects within the dia phragm or cylinder(3). I

In our preferred form of apparatus we proposed to make the vessel (1),diaphragm (3), anode (5) and false bottom (20) of graphite, the graphitevessel (1) serving as the cathode. In this way, the bath of electrolytecontacts only with graphite and the objectionable formation of Cul whencopper is used instead is avoided.

The present invention is not limited to the specific details set forthin the foregoing examples which should be construed as illustrative andnot by way of limitation, and in view of the numerous modificationswhich may be aflected therein without departing from the spirit andscope of this invention it is desired that only such limitations beimposed as are indicated in the appended claims.

W e claim as our invention:

When a test of the 1. In an electrolytic apparatus formal:- ingfluorine, a graphite vessel for holding a bath of electrolyte andconstituting the cathode, an anode of hardcarbonaceous materialprojecting into said vessel, means tori-" collecting the fluorineevolved at the anode comprising a diaphra surroundinggsaid anode, andmeans for lnsulating the ancde from the cathode and diaphragm and'fcrpreventing the escape of fluorine whrc,

anode enters said diaphragm. 2. In an apparatus for making fluorinet, acathode comprising a vessel, an anode of hard carbonaceous materialprojecting said vessel, a diaphragm su rroundlngsaid 0,,

a cathode comprising a graphite vessel, a graphite anode projecting intosaid vessel,

a diaphragm surrounding said anode, said diaphragm having openings nearthe lower extremity of the portion within the vessel and means forinsulating the anode from the cathode and diaphragm and for preventingthe escape of fluorine where anode enters said diaphragm.

'4. In an electrolytic apparatusfor mak ing fluorine, a vessel forholding a bath of electrolyte and constituting the cathode, an anode ofhard carbonaceous material projecting into said vessel, means forcollecting the fluorine evolved at the anode comprising a diaphragmsurrounding said anode, means for insulating the anode from the cathodeand diaphragm and for preventing the escape of fluorine where anodeenters said diaphragm, and means for heating the bath in a substantiallyuniformly, distributive manner.

5. In combintion an anode compartment comprising means for collectingthe fluorine evolved at the anode including a diaphra having openings atone end, saidanode eing of hard carbonaceous material, a cathode in theform of a vessel for holding an electrolyte, means for insulating theanode from the cathode and diaphragm and for preventing the escape ofgas liberated at anode where the anode enters the anode compartment, andmeans for heating the bath in a substantially uniforml distributivemanner.

6. In an electrolytic rocess of making fluorine with the aid of a hardcarbona' ceous anode, heatin a fluoride in avessel the said vesselconstituting the cathode and the heating being at a temperature at whichthe anode is substantially unattacked by fluorine and substantially,uniformly distributed throughoutthe electrolyte without causingobjectionable local heating.

llllti 7. In an electrolytic process of making fluorine with the aid ofa graphite anode, heating a fluorinde in a graphite vessel, the saidvessel constituting the cathode and the heating being at a temperatureat which the anode is substantially unattacked by fluorrine andsubstantially, uniformly distributed throughout the electrolyte withoutcausing local heating.

8. In an electrolytic process of making fluorine with the aid ofgraphite anode, heating an acid-alkali metal fluoride in a graphitevessel, the said graphite vessel con stituting the cathode and theheating being substantially, uniformly distributed throughout theelectrolyte without causing objectionable local heating.

9. A process of makin fluorine comprising electrolyzing a fused fluoridewith an anode and cathode made of hard carbonaceous material and at atemperature at which the anode is substantially unattacked by fluorine.I

10. In a process of making fluorine, electrolyzing a fused fluoride withan anode and cathode made of graphite and at a temperature at which theanode is substantially unattacked by fluorine.

11. A process comprising the electrolysis with a hard carboneous anodeand a hard carbonaceous cathode of an acid alkali metal fluoride in astate of fusion and collecting the evolved fluorine.

12. A process comprising the electrolysis with a graphite anode andgraphite cathode of an acid alkali metal fluoride in a state of fusionand collecting the evolved fluorine.

13. A process of making fluorine comprising dehydrating a fused fluoride{by means of a current of low current density and then increasing thecurrent density to that required for electrolysis.

14. A process of making fluorine comprising dehydrating a fused fluoridewith a current of low current density and with an anode of hardcarbonaceous material and then raising the current density to thatrequired for electrolysis.

15. A process of making fluorine comprising dehydrating a fused fluoridewith a current of low current density and with an anode of graphite andthen raising the current density to that required for electrolysis.

16. A process of making fluorine comprising dehydrating a fusedacid-alkali metal fluoride by .means of a current of low 7 currentdensity and then increasing the current density to that required forelectrolysis.

17. A process of making fluorine comprising dehydrating a fusedacid-alkali metal fluoride with a current of low current density andwith an anode of graphite and then raising the current density to thatrequired for electrolysis.

FRANK O. MATHERS.

BURR HISTON.

